The present invention generally relates to local area network (LAN) connection methods, and more particularly to a LAN or inter-LAN connection method which runs an existing LAN application in an asynchronous transfer mode (ATM) network and connects LANs.
As a means of structuring a LAN using the ATM technology in a broadband integrated services digital network (B-ISDN), a LAN emulation (LANE) protocol has been announced from the ATM Forum. The LANE inserts a media access control (MAC) protocol of the data link layer between the network layer protocol and the ATM protocol, similarly to the existing LAN such as the ethernet, so as to enable ATM communication without the need to modify the network layer protocol.
In order to run an existing LAN application in the ATM network which is based on a 1:1 (or point-to-point) communication, it is necessary to provide a mechanism to realize a broadcast function and the like which are characteristics of the LAN. The LANE protocol is characterized in that a plurality of connections are combined in the ATM network that provides a connection type communication which makes the communication by connecting subscribers, so as to make it look as if a connectionless type LAN communication were realized.
According to the LANE protocol, the MAC protocol of the data link layer is provided between the network layer protocol and the ATM protocol, similarly to the existing LAN, so that the ATM communication is realized without modifying the network layer protocol. A communication between LAN emulation client (LEC) terminals within an emulated LAN (ELAN) is realized by the following 3 servers, namely, a LAN emulation configuration server (LECS), a LAN emulation server (LES) and a broadcast and unknown server (BUS).
The LECS controls a LAN emulation address resolution protocol (LE ARP) and mainly copes with the address from a MAC address to an ATM address. The LES has a function of linking the individual LEC to a specific ELAN. The BUS transmits traffic with unknown destination, multicast traffic, and broadcast traffic to all the LECs within the segment.
When the end user terminal, that is, the LEC, transmits data, the LEC must known the network layer address (IP address) and the MAC address of the LEC at the other end, similarly as in the case of the conventional LAN. Further, the LEC must also know the ATM address (VPI/VCI) of the LEC at the other end. The LES notifies the ATM address of the LEC at the other end to the LEC, and the LECS notifies the address of the LES.
FIG. 1 generally shows a conventional system including LECs 1A and 1B, an ATM switch 2 connecting the LECs 1A and 1B, a LES 3, a LECS 4, a BUS 5, and a buffer 5d provided within the BUS 5. A connection L1 is made between the LEC 1A and the LECS 4, a connection L2 is made between the LEC 1A and the LES 3, a connection L3 is made between the BUS 5 and the LECs 1A and 1B, and a connection L4 is made between the LEC 1A and the LEC 1B. A connection procedure with respect to the ELAN of the system having the above described construction is as follows.
First, when the power of the LEC 1A is turned ON, the LEC 1A recognizes its own TM address and the ATM address of the LECS 4. The LEC 1A makes the connection L1 between the LEC 1A and the LECS 4, and obtains the ATM address of the LES 3 from the LECS 4. Next, the LEC 1A makes the connection L2 between the LEC 1A and the LES 3, and obtains the ATM address of the BUS 5 from the LES 3. Then, the LEC 1A makes the connection L3 between the LEC 1A and the BUS 5.
Next, a description will be given of the communication procedure. In order to know the ATM address of the LEC 1B at the other end, the LEC 1A issues a LE ARP request with respect to the LES 3 using the connection L2 so as to request notification of the MAC address of the LEC 1B at the other end. The LEC 1A sends the data to be transmitted with respect to the BUS 5 using the connection L3 even while waiting for a response to the LE ARP request from the LES 3. The data to be transmitted are successively stored in the buffer 5a.
Even if the BUS 5 does not know the ATM address of the LEC 1B at the other end, the BUS 5 transfers the data to the LEC 1B at the other end by broadcasting the data within the ELAN. The data transmission is made before the direct connection L4 between the LECs 1A and 1B is acquired, so as to eliminate a delay when acquiring the connection, and to make it look as if a connectionless communication is being made. When the LEC 1A receives the response (the ATM address of the LEC 1B at the other end) to the LE ARP request from the LES 3, the LEC 1A acquires the connection L4 between the LEC 1A and the LEC 1B at the other end. When this connection L4 is acquired, the LEC 1A sends the data directly to the LEC 1B at the other end without going through the BUS 5.
One LES and one BUS are set up in the ELAN, and both the LES and the BUS only manage the ATM address of the LECs in the ELAN to which the LES and the BUS belong. For this reason, according to the conventional LANE protocol, it is only possible to carry out a communication within the LAN. In order to make a communication (inter-LAN communication) between the LECs belonging to different ELANS, it becomes necessary to carry out a routing in the network layer by use of a router or the like.
FIG. 2 generally shows a conventional connection of ELANs. More particularly, FIG. 2 shows a case where a communication is made between LECs of an ELAN 101 and an ELAN 102. In FIG. 2, the LEC 1A, a LES 3-1, an ATM switch 2A and a BUS 5-1 are provided within the ELAN 101. On the other hand, the LEC 1B, a LES 3-2, an ATM switch 2B and a BUS 5-2 are provided within the ELAN 102. A router 6 connects the ELAN 101 and the ELAN 102.
Each of the LECs 1A and 1B is made up of a network layer, a MAC layer, a LANE and an ATM layer, starting from the upper layer. The router 6 is made up of a network layer, a MAC layer, a LANE and an ATM layer, starting from the upper layer.
In the system shown in FIG. 2, the LEC 1A issues a LE ARP request with respect to the LES 3-1 so as to know the ATM address of the LEC 1B at the other end, and attempts to recognize the MAC address of the LEC 1B at the other end. However, since the LES 3-1 does not know the ATM address of the LEC 1B at the other end, the LES 3-1 instead notifies the MAC address of the router 6 to the LEC 1A. During this time, the LEC 1A sends the data with respect to the BUS 5-1. Because the BUS 5-1 does not have a connection with the LEC 1B at the other end, the BUS 5-1 transfer broadcast data to the router 6. Then, the LEC 1A makes a connection between the LEC 1A and the router 6.
On the other hand, the router 6 receives the data from the LEC 1A and stores the received data in an internal buffer thereof. This router 6 transfers the data to the BUS 5-2 in place of the LEC 1A, and transfers the data to the LES 3-2 in place of the LEC 1A. When the router 6 recognizes the ATM address of the LEC 1B at the other end in response to the LE ARP request from the LES 3-2, the router 6 makes a connection between the touter 6 and the LEC 1B. Hence, the LEC 1A and the LEC 1B exchange the data via the router 6.
Therefore, according to the conventional system, it is not possible for make a direct connection (virtual channel connection: VCC) when making the communication between the LECs 1A and 1B in the different ELANs 101 and 102, and a complicated routing process is required by the router 6 in the network layer. As a result, a high-speed communication cannot be realized due to the need to carry out the complicated routing process in the router 6, and there was a problem in that the capabilities of the ATM network cannot be utilized efficiently when making an inter-LAN communication.